Automotive air conditioning systems can be divided roughly into two categories based on the type of expansion valve assembly used to expand and drop the pressure of the liquid refrigerant before it enters the evaporator. This distinction, in turn, determines the manner in which a system reserve of liquid refrigerant is stored, dried and filtered of contaminants. The subject invention relates especially to refrigerant filtering.
One common type of refrigerant expansion valve is a fixed, small diameter orifice, typically a brass tube held by a centering plug within the liquid refrigerant line. These are inexpensive, with no moving parts, but are obviously incapable of changing size to adapt to differing system demands. Such systems generally use a so called accumulator canister to store the refrigerant reserve with vapor only being pulled from the top of the canister to the compressor. Refrigerant drying desiccant bags can also be installed in the accumulator. Fixed orifice valves also provide a convenient location for a refrigerant contaminant filter screen, which can be secured to the centering plug to surround the orifice tube and filter the refrigerant as it flows through the tube.
The other basic type of expansion valve is an active, thermostatic expansion valve, in which the size of the expansion orifice can be actively varied, depending on system parameters and demands. An example may be seen in U.S. Pat. No. 4,342,421, which is often referred to as a TXV system. With a TXV system, it is most efficient if only liquid refrigerant be fed to the expansion valve, so it is convenient to store (and dry) liquid refrigerant reserve in a so called receiver-drier canister located just upstream of the valve. The more complex TXV valves, with their moving parts and small internal passages, are not convenient locations for direct incorporation of a refrigerant filter, which may be placed instead in the receiver-drier canister. As receiverdryers have become more compact, however, and sometimes integrated directly into the return header tank of the condenser, there is less room for filter installation. Moreover, a receiver canister is generally not easily opened or disconnected to allow a filter to be serviced or removed, if at all.
A recent U.S. Pat. No. 5,562,427, claims a refrigerant filter of a specific material and pore size, and discloses it in numerous possible locations, including the receiver, refrigerant line, and compressor housing. The filter design itself is not particularly amenable to handling, installation or removal, having several parts. In addition, every installation location disclosed would require some major modification to the existing air conditioning system and components.
It is generally necessary in any vehicle air conditioning system, or at least convenient, to be able to reversibly attach and detach both refrigerant lines (the liquid supply line into the evaporator, and the suction or gas line out of the evaporator) from the evaporator, both for initial installation and for later servicing or removal of the evaporator. This is conveniently done with block connections, in which two or more blocks or plates are bolted together to simultaneously join four line ends (two ends for each line) in sealed communication. In one block connector design, the line ends are solidly brazed down into bores formed in end fittings, which are then bolted together into bores in a block, as in U.S. Pat. No. 5,354,101. In another, the four line ends are instead pulled toward one another and into a central block by two side plates, which act as clamps. The line ends are not solidly fixed to the side plates, however. Instead, the side plates bear against the outside of enlarged beads on the lines, which are set back from the terminal edges of the line ends. In either case, when the block fitting is disconnected, the ends of the lines, or at least the ends of the fittings to which the lines are fixed, are visible and accessible. One design in which the filter of the invention may be conveniently installed is disclosed in U.S. Pat. No. 5,467,611, which uses a central block and side plates.